I'm reasonably sure this isn't the case. Even in pure math, postdoc salaries tend to start at $50k ($45k in low cost of living areas like Urbana Champaign). Associate (tenure track, but not yet tenured) profs tend to start at $70k. I can guarantee you engineering/CS makes significantly more.
However, the average professor makes very little, because the average professor (of, e.g., Medieval English Literature) has few marketable skills.
However, the average professor makes very little, because the average professor (of, e.g., Medieval English Literature) has few marketable skills.